A line-of-sight gaming system operates with cashless transfers between a cashier and gaming machines. A player gives money to a cashier who instructs the system to place credits on the players selected machine. The gaming machine is (or should be) in the cashiers line-of-sight so they can see the machine is not currently being played and that once the players has paid that no one else uses the machine.
Aristocrat Technologies operated a line-of-sight cashless system called BIPS in New South Wales, Australia in the 1990's.
A disadvantage of these systems is that the number of machines on the gaming floor is limited to those visible to the cashier.
Gaming machines may have a reservation button, enabling players to reserve a gaming machine for their use. The player presses the reserve button and the gaming machine enters the reserve mode, and displays a reserve message. When the reserve button is pressed again the machine exits the reserve mode.
U.S. Pat. No. 5,429,361 describes a gaming system in which a magnetic card is used as a reservation lock. This patent describes to a traditional gaming system using magnetic cards, where the reserve key only works when the player's magnetic card is inserted. If they press reserve, then remove their card the machine cannot be unreserved until the card is reinserted. After a predetermined timeout period the machine will automatically unreserve. This is ideal for players to take short breaks without the possibility of someone else stealing their money.